Along with the continued and increasing use of video displays has been the problem of the man/machine interface. Traditionally, control of displayed information or cursors has been via the use of a keyboard. More recently, however, a number of devices have been introduced which allow an operator to directly interact with a video display. These devices have included light pens, desk-type mouse controllers, or touch input devices, such as a switch matrix or opto-electronic matrices. While switch-type overlays, placed adjacent a video display, are generally inexpensive to apply and to utilize, they are also susceptible to contact wear as well as the distortion of the video information which is presented to the viewer or operator, particularly in situations involving a high degree of use. Opto-matrix schemes utilizing light which is generally in the infrared region, however, create a switch matrix which is invisible to the viewer or operator and, therefore, does not distort the video information displayed and is not subject to wear in high use environments. Systems utilizing opto-matrix frames are well known in the art. Examples of such systems include U.S. Pat. No. 4,267,443, entitled "Photoelectric Input Apparatus," issued May 12, 1981 , to Carroll, et al., and U.S. Pat. No. 4,684,801, issued Aug. 4, 1987, to Carroll, et al., entitled "Signal Preconditioning For Touch Entry Device."
Such systems address problems inherent with the use of opto-matrix devices such as increasing frame resolution without a corresponding increase in the number of components used, surrounding or ambient light compensation, and the optimization of emitter/detector driving and detecting networks. Such systems, however, still have drawbacks. For example, the use of a large number of components results in higher costs. Additionally, some systems exhibit difficulty in compensating for reflection or glare, which sometimes results in the failure of the system to detect a touch or hit.
Glare problems generally occur when an emitter is adjacent a corner of a frame or bezel so that, when the emitter produces light, the light so produced bounces off an adjacent surface and is then detected by a detector corresponding to the emitter. A stylus or other object which is introduced to the video display may block the majority of the light received by the detector, but the amount of reflected light or glare may be sufficiently great whereby the detector and the system do not detect a hit or the presence of an element.
Ambient light also results in significant problems in such touch entry systems. Several systems for compensating for ambient light problems have been proposed and are marketed in touch entry systems. For example, U.S. Pat. No. 4,267,443, entitled "Photoelectric Input Apparatus," issued May 12, 1981, to Carroll, et al., discloses an ambient light sampling system. Additionally, U.S. Pat. No. 4,243,879, entitled "Touch Panel with Ambient Light Sampling," issued Jan. 6, 1981, to Carroll, et al., discloses an ambient light sampling system in a touch entry system.
It is desirable to have a touch entry system which minimizes the number of components necessary for addressing and sampling light emitters and light detectors. It is also desirable that the device dynamically compensate for ambient light effects and for variations in emitter light output and detector sensitivity. At the same time, however, the device should employ a minimal number of components. Accordingly, it is an object of the present invention to provide a touch entry system which minimizes the number of components necessary for accurately addressing and sampling light detectors and light emitters surrounding an irradiated field.
Other ambient light compensation systems have required the use of large amounts of energy to drive light emitting devices, such as infrared light emitting diodes (LED's), in order to ensure that the intensity of the light emitted by the LED's is greater than the intensity of the ambient light. Such an approach requires the use of expensive light emitting and light detecting elements. Such an approach also requires that even high performance LED's and phototransistors be operated outside normal operating ranges.
The use of modulated light pulses in a touch entry system allows more accuracy and confidence in the determination of whether or not an element is present in the field and blocking one or more light detectors. The frequency of the light pulses emitted by the light emitters in such a system can be preselected easily so that the pulse frequency is markedly different from the various frequencies of ambient light usually present in a variety of environments.
It is an object of the invention to provide a touch entry system which utilizes modulated light pulses to provide increased accuracy and confidence in the determination of the presence of an element in an irradiated field.
It is a still further object of the invention to provide a practical touch entry device comprising a four-sided substantially rectangular frame with optical emitters and detectors disposed in the sides of the frame with a device for sequentially sampling and activating the light detectors and light emitters.
A still further object of the invention is to provide a cost effective device to overcome ambient light problems in a touch entry system by utilizing and detecting modulated light pulses.
It is a still further object of the invention to provide a touch entry system which compensates for ambient light effects which is easily manufactured and produced with a minimum number of components and at a minimal cost.